CA2098521 discloses a method for producing a high-grade nickel matte and a highly oxidized slag in a flash smelting furnace, and for reducing the slag from the flash smelting furnace and for sulfidizing the resulting matte in an electric furnace. The matte produced in the flash smelting furnace and in the electric furnace are both directly conducted to further hydrometallurgical treatment. The method consists of drying, flash smelting, slag cleaning, and sulfurizing in one or two electric furnace(s) and gas cleaning for all the process step. This method requires much energy for drying, much technical oxygen for smelting and much energy for producing technical oxygen and oil or other fuel for smelting. This method requires also coke or other reductant for slag cleaning. The use of organic fuel and reductants in this process produces significant amounts of CO2 emissions. This process produces two different types of matte: matte from smelting and matte from reduction. This means, that also two different leaching processes are required. Use of fuels increases the amount of gas flow and the big gas flow requires big boiler and gas line. Further, the smelting step requires high temperatures and furnace walls much cooling water.